Wave signaling system



Nov. 29, 1932. J. ROBINSON WAVE SIGNALING SYSTEM Filed July 30, 1929 2 Sheets-Sheet l Nov. 29, 1932. J. ROBINSON 1,839,293

.WAYE SIGNALING SYSTEM Filed July so, 1929 2 Sheets$heet 2 urina Patented Nov. 29, 1932 UNITED STATES PATENT; OFFICE 1 JAMES ROBINSON, OF MILL HII'L, ENGLAND, ASSIGNOR, BY MESNE ASSIGNMENTS, TO

BRITISH RADIOSTAT CORPORATION, LIMITED, A' CORPORATION OF CANADA WAVE. SIGNALING SYSTEM Application filed July 30, 1929, Serial No. 382,258, and in Great Britain August 10, 1928.

This invention relates to wave signaling systems such, for example, as high frequency electric systems for radiotelegraphy, radiotelephony, whether effected over an electrically conducting circuit or without tangible connection between signaling stations; In such systems a plurality of channels of communication is provided by the use of a plurality of carrier waves of diiferent car rier or basic frequencies and signals are effected by changing the amplitudes of or nterrupting the carrier waves, or by slight ly changing the basic frequency thereof.

It is generally supposed that for satisfactory communication the resonant apparatus employed should be broadly tuned, that is to say have a reasonably uniform response to the plurality of frequencies thus associated with a carrier frequency.

The inventioncomprises a system of wave signaling in which there is employed a resonant apparatus to deal with modulated wave forms, which has a high degree of se-' lectivityof the order that is obtained by a piezoelectric device or a still higher selectivity.

Usually selectivity is improved by reducing the damping, but if the damping is reduced sufficiently to'produce the required selectivity, there is involved a phenomenon which may be called persistence of oscillation, meaning the continuance. of an oscillation in a resonant oscillatory apparatus after the excitation which set up the oscillation has ceased. It is obvious that the lower the excitation of a reversed phase.

high speed of signaling, and in the case of radio telephony, to maintain a faithful reproduction at the receiver of the signal applied to the transmitter. 7

An object of this invention is to provide a system in which these desirable qualities of selectivity and the accompanying efficiency are coupled with the facility for high speed telegraphic work and faithful telephonic reproduction.

The present invention comprises a system of wave signaling in which the damping of a resonant apparatus employed therein is less than that normally required for true reproduction of the'initial si nals and by the control of the energy in said resonant apparatus true reproduction is obtained therewith. i

The damping above expressed as less than that normally required for true reproduction may be characteristic of an oscillatory apparatus vhaving slight positive,- zero or even negative resistance and the term true reproduction. herein means the reproduction that is obtained when the energy in the os- Y in combination with means f'orquickly stopping out, either periodically or at predeter- 'mined'times, oscillations therein which have been setup by excitation of the apparatus. By this means full use is made of the hlgh selectivity of resonant oscillatory apparatus of low damping, but on the other hand, the persistence of oscillation, after the cessation of the excitation, is minimized.

One method of damping out the oscillations consists in intermittently introducing Thus a source of high frequency energy may be applied, in two phases that are opposed, to the the period only when excitation of the resonant oscillatory apparatus is required and the other may be rendered active only when I the damping out of an oscillation already I in telephony or allied signaling. mg this invention to carrier'wave telephony set up in the resonant oscillatory apparatus is required. The periods of excitation in one phase and in the other phase of course need not be equal but will depend largely upon the characteristics of the oscillatory appaeither amplitude or frequency modulation may be employed.

The invention may be applied either to the tran-smitt r or to the receiver of a high frequency electric signaling system or to and The accompanying drawings illustrate diagrammatically as examplesrseveral ways of carrying the nvent on intoettecth In the drawings Figure 1 is a simplecircuit arrangement, Figure 2 shows curves indicating the rise f and fall of energy in typical oscillatory apparatus of different damping.

Figures 3, it and 5 are curves showing the manner of controlling the oscillatory apparatus according to the invention.

Figure 6 is a diagram of a receiver embodying the invention.

Figure 7 is a diagram of a transmitter.

Figure 8 is a diagramof a receiver embodying'aresonator with negative resistance,

Figure 9 is a diagram of a transmitter with two aerials.

Referring to Figure 1, a source of oscillator energy 10 (in this case-electric energy) by means of which signaling is effected, .is fed through coils 11 and 12 to a resonant oscillatory circuit13, the arrangement of the coils 11 and 12 being such that the two resulting inputs to the oscillatory circuit 13 are opposed in phase.

The oscillatory circuit13. includes a piezoelectric crystal 15 by means of which a high order of selectivity is obtained. By known means here shown simply by a key 141: for example (the valves .and tuning apparatus usuvally employed having been omitted) energy is fed to the oscillatory circuit 13 by the coil 11 When excitationof the apparatus is required and the other coil 12 is energized during the intervening periods to damp out .os-

cillations previously set up'by the coilv 11.

Alternatively, the reversal of phase of the excitation may be obtained by effecting a small change of frequency of the excitation has the lowest damping.

with the use of intermediate oscillatory apparatus sharply tuned to the mean of the excitation frequency.

Referring to Figure 2, there are shown apilied on a time axis OX a ainst an axis F L O, Y representing amplitude n the resonant circuit, three curves 16, 17 and 18 representing the rise and fall of energy in three typical circuits of which that giving the curve 18 of this invention apparatus having a characteristic such as indicated by the curve 18 is chosen,'the time which would be taken for excitation of this apparatus to die away with only its inherent damping, is much greater than the permissible time between successlve signals, particularly in high speed signaling, and therefore a control of the energy iii the oscillatory apparatus is necessary. If for instance by excitation of the apparatus the energy builds up to the point 38 on curve 18 the time O39 for the excitation to die away due to the inherent damping is greater than is permissible but by control of the energy this time canbe reduced to a satisfactory low to build up for say cycles, and then is reducedin another period of say-5O cycles by the application of the excitation in opposite phase. 1

Thus, for continuous wave excitation there isobtained as shown in Figure 3, a period of positive excitation 19 obtained for example by means of the coil 11 in Figure 1, followed by a period of negative excitation 20 of opposite phase obtained by means of the coil 12. These periods alternate regularly and the resultant effect, as shown in Figure 4, is a succession of impulses 21 equal in length to the sum of a positive period 19 and a negative period 20. These impulses 21 ar constituted by'the rise and fall of energy in the oscillatory apparatus due respectively to each positive excitation 19 and the following negative excitation 20.

In the examples given above it has been assumed that the oscillatory apparatus has a slight positive resistance, but as previously stated, the apparatus may have zero or negative resistance. In the latter case if the negative impulses 20 are equal to the positive imthe variation due to the signals are imposed.

It will be understood that the periods of ex- If for the purpose AAJU citation of the oscillatory apparatus by the cuit such as the damping. For example 1 when the oscillatory apparatusv has slight positive resistance, then the impulses need not be as long as the impulses 19 in order to bring the apparatus to a quiescent state at the end of each one of the signal impulses 21.

In applying the invention to a. receiver, in the example illustrated in Figure 6 an antenna system is connected to the control electrodes and cathodes of two thermionic valves 31 and 32 in parallel with one another. The anodes of the two thermionic valves may be respectively connected through coils 33 and 34 to opposite electrodes associated with a piezoelectric crystal 35 which is accurately tuned to the carrier or basic frequency used for signaling which may be forv example 10 or 10 The anodes are also connected respectively to opposite ends of an inductance 56 the centre point of which is connected to the positive pole of a D. C. supply 38 the negative of which is connected to the cathodes of ing current. If desired,bias batteries may be connected in circuit with the anodes of the valves so as to render the periods of operativeness of the two valves unequal. It will be observed that the potential variations at the anodes of the two valves are in the same phase but that these are applied oppositely to the piezo-electric crystal. However, at any instant only one of the valves is in operation and during that time oscillations are set up in the piezoelectric crystal, which oscillations are reduced and stopped during the time that the second valve is in operation.

The piezo-electric crystal is a very highly selective resonant device and is only responsive to frequencies very close to that frequency to which it has been tuned. Consequently incoming signal frequencies different from that to which the piezo-electric crystal is tuned have little or no elfect upon the crystal and he receiver is therefore rendered highly selective by the crystal but since the oscillations of the crystal are periodically stopped, the receiver is not subject to the defects caused by persistence of oscillation. One or both of the coils which are connected in series with the crystal may be coupled to a detector and receiver of conventional type as indicated diagrammatically in Fig. 0 of the drawings. In Figure 6 the source of alternating current 37 for producing the difference in phase is applied to the anode circuits of the valves 31 and 82; it may alternatively beapplied to the grid circuits. I

It'will be understood that although in the examples described a piezo-electric crystal in conjunction with apparatus of lowvdecrement is utilized, other equivalent means may be employed such for example as a thermionic valve system brought to a state of low damping or even negative resistance by the use of reaction.

In Figure 8 there is shown, by ,way ofexample, -a receiver which is similar to that shown in Figure 6 with the exception that instead of a piezoelectric crystal 35, there is employed-a resonator consisting of a retroactive thermionic valve system 41 having negative resistance. This thermionic valve system is energized by means of a coil connected between the anodes of the receiving valve 31, 32 and has output terminals for the signals at 42.

In applying the invention in one form of" transmitter for telegraphy or telephony, there are employed (see Figure 7) two oscillatory circuits and 51, which are tuned to the basic or carrier frequency and are shown as output circuits of thermionic valves 22 and 23 respectively so arranged that the circuits are excited in opposite phase. The input circuit of the valves indicated at 24 may be coupled in any suitable manner to the source of high frequency energy used for signaling.

The two oscillatory circuits 50 and 51 are coupled by means of electromagnetic couplings 25 and 26 respectively to a circuit 27 energized by a controlling frequency of say 15,000 to 20,000 cycles per second. The arrangement is such that the two oscillatory circuits 50 and 51 are oppositely modulated, that is when the amplitude of one oscillatory circuit is at a maximum that of the other oscillatory circuit is a minimum, and vice versa.

The resultant radiated energy therefore will change in phase rhythmically and by employing a controlling frequency of about 15,000 to 20,000 cycles per second asabove mentioned the rhythmic changes of phase are above audibility. The amplification to be obtained can be as large as is required. I

The oscillatory circuits may be radiating systems or they may be coupled to one or more radiating systems. If a single radiating system is used as shown at 28, the oscillations caused by one half-cycle of the controlling frequency will be quickly damped 1 outloy the excitation by the other oscillatory circuit during the other half-cycle.

The oscillatory circuits 50 and 51 may be arranged to energize two separate radiating systems 43 and 44 as shown in Figure 9 which ISO indicates a transmitting apparatus which is similar in other particulars to that shown in Figure 7. The aerlals 43 and 44: are spaced apart and in this case oscillations set up by one radiating system will be properly counteracted by a succeeding train of oscillations from the other radiating system in certain definite directions with respectto the positions of the radiating systems. These radiating systems might be beam aerials.

The invention is particularly applicable to systems employing frequency modulation as described in British specification No. 295,- 957 in which modulation is effected Within the limits of frequency to which a piezoelectric crystal is responsive, that is to say, about cycles.

In applying the present invention continu ous wave energy is propagated from a transmitter and a speech or other form of signal variations is caused to vary the frequency of the continuous wave energy within the narrow limits above indicated. 7 V

The frequency modulated energy is reversed inphaseperiodically according to one feature of this invention either at the transmitter or at thereceiver. Vith a receiver such as that indicated in Figure 6, there are obtained periods of positive and negative eX- citation as indicated in Jigure .3 signal impulses as indicated in Figure at; for telephony the frequency ofthese latter impulses should be in excess of 10,000 cycles per second.

The modulation of the transmitted energy causes its frequency to be varied up and down say 10 cycles per second at the frequency of the signalin note, say 1000. The piezo-electric crystal of the receiver is adjusted with reference to the mean frequency of the oscillatory energy and since this frequency is varied by the modulation, the piezoelectric crystal responds to a greater or lesser extent depending upon modulation. The response of the piezoelectric crystal will thus follow the variations of the signaland consequently the amplitude of the impulses indicated in Figure 4 will rise and fall in magnitude in consequence of themodulation in this case at a frequency ofone value.

It will be appreciated that in order to receive the frequency modulated signals in which the range of modulation is a very narrow one such as that permissible with the ie'Zo-clectric crystal it is necessary that the receiver should be properly-responsive to system according to the invention as above described a piezo-electric crystal has been employed there may be alternatively used a valve system which is adjusted for example by means of reaction to have very little positive resistance and preferably zero or even negative resistance.

It-is to be understood that the invention is not limited to the particular ways of using or applying the wave energy in reverse phase to the si naling energy in order to control the latter as above described, for example the required damping of the oscillations may be effected in accordance with the movement of a keying device as is done in the curbing of submarine signals.

Also the invention is applied to any wave transmission whether electric or acoustic and duction so that oscillations tend to persist therein after the signal ceases, in combination with means for rhythmically altering the phase of the energy in the said resonant apparatus at a frequency lower than the carrier frequency of the received energy and higher than the highest modulation frequency of the received energy in order to subdue the persisting oscillations in the said resonant apparatus.

2. A receiver for wave signals comprising a resonant apparatus having a negative resistance characteristic such that free oscillations are set up therein and means for altering periodically the phase of the energy in the said resonant apparatus for the purpose of quenching the oscillations.

3. Areceiver for wave signals comprising a resonant apparatus having a negative resistance characteristic such that free oscillations are set up therein and means for periodically reversing the phase of the energy in the said resonantapparatus for the purpose of quenching the oscillations.

if. A receiver for wave signals comprising a resonant apparatus having a negative resistance characteristic such that free oscillations are set up therein, means for applying the Wave energy to the resonant apparatus in two phases that are opposed and means circuits alternately operative upon the resonant apparatus at a frequency that is greater than the signal frequency.

6. A receiver for wave signals comprising a resonant apparatus having a negative re sistance characteristic such that free oscillations are set up therein, two input circuits arranged to be excited by the received signals in two phases which are opposed and are fed to said resonant apparatus and means for applying a subsidiary wave to said input circuits to produceopposite effects therein at any instant whereby said input circuits are rendered alternately operative upon the resonant apparatus to quench the oscillations therein.

7. A wave signaling system comprising a transmitter of wavesignals, a receiver for said wave signals, said receiver having a resonant apparatus that has abnormally low damping so that oscillations tend to persist therein after the signalceases with consequent signal distortion, and means in the system for rhythmically changing the phase of the wave energy that is effective in the reso nant apparatus at a frequency differing from the frequency of the signals whereby the persisting oscillations are subdued and true reproduction of the slgnals is obtained.

8. A wave signaling system comprlslng a transmitter of wave signals, a receiver for said wave signals, said receiver having a resonant apparatus that has abnormally low damping so that oscillations tend to persist I therein after the signal ceases with consequent signal distortion, and means at the receiver for rhythmically changing the phase of the energy in the resonant apparatus whereby the persisting oscillations are subdued and true reproduction of the signals is obtained.

9. A wave signalingsystem comprising a transmitter of wave signals, a receiver for said wave signals, saidreceiver having'a-resonant apparatus that has abnormally low damping so that oscillations tend to persist therein after the signal ceasesfwith consequent signal distortion, and means at the transmitter for rhythmically changing the phase of the energy that is transmitted at a frequency differing from the frequency of the signals in order to produce a corresponding change of phase in the received energy in the resonant apparatus, whereby the persisting oscillations are subdued and true reby the persisting oscillations are subdued and true reproduction of the signalsis obtained.

11. A wave signaling system comprising a transmitter for wave signals, a receiver for said wave signals, said receiver having a resonant apparatus that has abnormally low damping so that oscillations tend to persist therein after the signal ceases with conse quent signal distortion, and means at the transmitter for periodically reversing the phase of the energy that is transmitted at a frequency differing from the frequency of the signals in order to produce a corresponding periodic phase reversal of the received energy in the said resonant apparatus, whereby the persisting oscillations are subdued and true reproduction of the signals is obtained.

12. In a receiver for wave signals, the combination with a resonant apparatus that is stable but has abnormally low damping so that signal oscillations tend to persist therein after the signal ceases with consequent signal distortion, of means for altering the phase of the energy in the said resonant apparatus in order to subdue the persisting oscillations therein and to obtain true reproduction of the signals. 7

13. A receiver for wave signals comprising a resonant apparatus that is stable but has abnormally low damping so that signal oscillations tend to persist therein after the signal ceases with consequent signal distortion, in combination with means for intermittently reversing the phase of the energy in the resonant apparatus in order to subdue the persisting oscillations therein and to obtain true reproduction of thesignals.

14. A wave signaling system comprising a transmitterflof wave signals, a receiver for said wave signals, said receiver having a resonant apparatus that has abnormally low damping so that oscillations tend to persist therein after the signal ceases with consequent signal distortion, and means in the system for rhythmically reversing the phase of the wave energy that is effective in the resonant apparatus at a frequency differing Elfi III

from the frequency of the signals whereby the persisting oscillations are subdued and true reproduction of the signals is obtained.

15. A wave signaling system comprising a transmitter of wave signals, a receiver for said wave signals, said receiver having a resonant apparatus that has abnormaly low damping so that oscillations tend to persist therein after the signal ceases with consequent signal distortion, and means at the receiver for rhythmically reversing the phase of the energy in the resonant apparatus whereby the persisting oscillations are subdued and true reproduction of the signals is obtained. 1

In testimony whereof I affix my signature.

JAMES ROBINSON. 

